I've decided to do a little bit of best-case scenario and worst-case scenario here with the roster.
I think I'm pretty sure that the roster for both versions (or at least if counting transformations around the same) going to be bigger then Brawl. But how big is what's the debate here. I believe there will probably be around 10-15 new characters in the game. I've split a prediction into whether the roster is bigger or less then 45
Also just in case you're confused. Already confirmed returning characters are not in this list for obvious reasons. It's public knowledge :P
Roster Number > 45
Captain Falcon- Original 12
Diddy Kong- Staying from Brawl
Falco- Was here since Melee, so probably would be here to stay
Ganondorf- Definitely staying
Ice Climbers- Sakurai likes them, plus Sakurai mentioned implementing them once.
Ike- He'd stay to represent the start of Fire Emblem going overseas
Jigglypuff- Original 12
King Dedede- Was probably among the most requested Nintendo newcomers before Brawl. Plus Sakurai could have more fun voicing him again.
Lucario- Still one of the few that even in a more optimistic view may still get cut simply because of this apparent need for at least one Pokemon from the new generation to get in. (Lucario technially not being the only one, it's just Lucario was recieved much, much better then Pichu's inclusion in Melee)
Lucas- Staying because he's different enough from Ness, plus Mother 3 is perhaps the most critically acclaimed out of the MOTHER series
Luigi- Original 12, Year of Luigi, etc.
Marth- The one for sure constant Fire Emblem rep. Staying
Meta Knight- Was quite a popular inclusion. Even for his infamy in the Competitive side of things. Staying
Mr. Game and Watch- Quirky, and probably the easiest of the veterans to animate. Staying
Ness- Original 12 (Plus more relevancy now that Earthbound is on the Wii U Virtual Console)
Peach- You're kidding yourself if you think Peach is going anywhere.
Pokemon Trainer- Plenty of questions here. In the best case scenario he'd probably be back, but will he have the same Pokemon? That's a different question entirely however
ROB- I think he'd be well enough to stay. Maybe even get a proper Gyromite stage of some sort.
Snake- Staying in this scenario as to respect his friend. Not to mention it's quite noticable that Snake didn't get into the Playstation game. Could Smash be the reason for that?
Sonic- I could bring up quite a few important points if you really think Sonic's chances of returning is any lower then 90%.
Toon Link- Like Lucario, even among more optimistic views Toon Link might be gone. Spirit Tracks Link doesn't necessarily automatically deconfirm him yet however, as Toon Link does have the Wind Waker remake in his favor.
Wario- Definitely staying
Wolf- It's actually 50/50 here. Wolf is quite iconic to Star Fox series. Arguably more so then Falco. But at the same time if Sakurai feels like Star Fox's reps need to be shrunken down for whatever reason. I think Wolf goes sooner then Falco unfortunately
Yoshi- Original 12
Zelda- Staying, probably with her Skyward Sword look. Shiek might be in question, although Twilight Princess having no Shiek didn't stop Zelda from having her transformation in Brawl.
Roster Number < 45 (10-15 Newcomers, but they have to shrink the returning Veteran list in order to do so, Roster close to or around 40)
Captain Falcon- No Change from Greater then 45
Diddy Kong- You could argue Diddy isn't as important and could be at least changed to pair up with Dixie and or outright replaced with K. Rool. But I don't think that's likely.
Falco- If anyone of the Melee veterans that returned in Brawl are being cut Falco would be it. But I believe because he was in the previous two game, his chances are fairly big.
Ganondorf- Eeeeeeeeeeeh, you could say he'd likely to be replaced by someone more relevent. (Or perhaps the character himself will change to a huge degree into the Pig ganon he was in the original games to a shocking less relevant form). Or replaced by Demise or even Ghirahim. But I like to think that as of Melee, Link, Zelda, and Ganondorf are the Triforce destiny pretty much and make the core of the Zelda reps in SSB. So I think he'd stay still.
Ice Climbers- No Change from Greater then 45, even with possible programming difficulty
Ike- Could possibly be cut in order to place someone like Chrom in
Jigglypuff- No change, though to be fair if anyone of the Original 12 found themselves being cut. Jigglypuff probably would be that one. Considering in Brawl, Jigglypuff wasn't the first character you unlocked. Jigglypuff could break "tradition" again by not even being in the game in the first place. But I think the new Fairy-type in X & Y makes her a little more relevant.
King Dedede- No Change from Greater then 45
Lucario- Being cut, no doubts about it
Lucas- I say it's 50-50 even with the worser scenario. But Ness will be the rep more likely if Mother must be restricted back to 1 representative
Luigi- No Change from Greater then 45
Marth- No Change from Greater then 45
Meta Knight- No Change from Greater then 45
Mr. Game and Watch- No from Greater then 45
Ness- No Change from Greater then 45
Peach- No Change from Greater then 45
Pokemon Trainer- Could be cut if it proves too difficult or if having multiple Pokemon makes Sakurai think he's over saturating the roster with Pokemon reps. But I wouldn't find it too hard to believe that his chances of staying are better then his doubters think.
ROB- I think he's most likely staying. But if one previous WTF character no one saw coming must go. ROB I think is gone first.
Snake- Probably gone, Brawl might of been a one-time deal for Snake at least. However I do think alot of people underestimate Snake's chances at times. That even if this situation happened I'd like to see the looks on people's faces if Snake and Sonic both returned despite the rather big size of cuts.
Sonic- No Change from Best Case Scenario, again I can argue why even in THIS scenario.
Toon Link- Yeaaaaaah, he's gone in this case :X
Wario- No Change from from Greater then 45
Wolf- Probably going, as arguably more iconic to Star Fox then he is to Falco. Falco has the advantage of being in 2 games to 1 compared to Wolf.
Yoshi- No Change from Greater then 45
Zelda- No Change from Greater then 45